In the past, almost all engines utilized inwardly opening valves to permit the exchange of gases with the engine's hollow piston cylinders between each combustion event. The valve member typically includes an enlarged portion with an annular valve face that is positioned within the hollow piston cylinder and a stem attached to the enlarged portion that protrudes away through the opening connecting the cylinder to a gas passageway. During combustion, these valve members are held against their seats by the high pressure differential existing across the valve opening during combustion. In most cases, these types of valves are pushed open between combustion events by a cam that is driven directly by the engine. While these types of cam driven inwardly opening valves have performed well over many years, the current trend toward electronically controlled valves may render the inwardly opening valves of the prior art unsuitable.
In the case of diesel engines, the timing of valve opening with the movement of the piston in its cylinder is critical because the piston and valve members must necessarily occupy the same space within the hollow piston cylinder, only at different times.
Although valve to piston contact is a possibility with prior art cam driven systems, it rarely occurs because the mechanical interconnection of the various components makes such contact extremely unlikely. In the case of electronically controlled and actuated valve members, piston contact is much more likely because there is no mechanical interconnection. In other words, potentially catastrophic valve to piston contact can occur simply because of an erroneous open command produced by the engine computer due to software errors and/or erroneous sensor inputs to the computer. Thus, the real and perceived danger of valve to piston contact with electronically actuated and controlled valves has hindered movement in the industry to a camless engine that is completely electronically actuated and controlled.
One method of avoiding the possibility of valve to piston contact is to utilize outwardly opening valves that are actually positioned outside the hollow piston cylinder and therefore do not have the possibility of valve to piston contact. However, outwardly opening valves have never been successfully implemented into diesel engines on a large scale because of the great difficulty in holding such valve members closed during the high pressures produced by combustion. In those cases where outwardly opening valves have been successfully utilized, the actuation system utilized to both hold the valve closed and open the valve at desired times often requires large amounts of energy, which again renders such a system less than desirable.
The present invention is directed to overcoming the problems of holding outwardly opening valves closed during combustion so that the current trend toward an electronically controlled and actuated valve system can continue.